Valves comprise at least one valve seat, a valve plunger and an actuator for moving the valve plunger relative to the, or each valve seat from, a first position of the valve plunger into a second position of the valve plunger.
In case of a 2-way-valve, the valve comprises usually one valve seat and the actuator moves the valve plunger for a closing operation of the valve from a first position, in which the valve plunger is lifted off from the valve seat, into a second position, in which the valve plunger is pressed against the valve seat. In said second position of the valve plunger of the 2-way-valve, a flexible element assigned to the valve plunger often needs to be compressed in order to provide tightness between the valve plunger and the valve seat.
In case of a 3-way-valve, the valve comprises usually two valve seats and the actuator moves the valve plunger of the valve for a combined closing/opening operation of the valve from a first position, in which the valve plunger is pressed against a first valve seat and lifted off from a second valve seat, into a second position, in which the valve plunger is lifted off from said first valve seat and pressed against said second valve seat. In both of said positions of the valve plunger of the 3-way-valve, a respective flexible element assigned to the valve plunger often needs to be compressed in order to provide tightness between the valve plunger and the respective valve seat.
In known valves having a stepper motor as an actuator, a driver is assigned to the stepper motor which drives the stepper motor in such a way that the stepper motor provides a defined number of steps in order to move the valve plunger from the first position into the second position and in order to compress the respective flexible element assigned to the valve plunger in said second position thereby providing tightness between the valve plunger and the valve seat. It is hereby necessary that the stepper motor is driven in such a way that even in view of tolerances of the valve, the tightness between the valve plunger and the valve seat can be provided. Such tolerances include the mechanical tolerance of the nominal valve distance between the first position and the second position of the valve plunger as well as tolerances in the behaviour of the respective flexible element being assigned to the valve plunger which is influenced by external factors like temperature and pressure.
To absorb such tolerances the stepper motor of known valves is typically driven in such a way that the defined number of steps provided by the stepper motor includes always a defined number of oversteps, whereby the driver operates the stepper motor for all steps of the defined number of steps including the oversteps at the same electrical current level. Such oversteps can create a bumping noise and vibrations in the valve. Further on, not needed oversteps consume electrical energy and reduce the life-time of the valve.